A lot of equipment used in various fields such as high-speed machine tools, air motors and actuators, compressors of the recent techniques require electric motors enabling high-speed operations exceeding 15,000˜20,000 rpm, and in some cases up to 100,000 rpm.
Most of high-speed electric devices are manufactured with low pole count, which is to prevent magnetic materials in the electric devices to operate at higher frequencies from leading to too excessive core losses. The main cause is in the fact that soft magnetic materials used in most of motors are made up of Si—Fe alloys. In the conventional Si—Fe-based materials, the losses resulting from a magnetic field changing at a frequency of about 400 Hz or more may heat a material until the materials may often not be cooled even by any suitable cooling means.
Typically, electric motors include magnetic members formed of a plurality of stacked lamination plates made of non-oriented electric steel sheets. Each lamination plate is typically formed by stamping, punching or cutting mechanically soft non-oriented electric steel sheets into a desired shape. The formed lamination plates are stacked over one another, to thus form a rotor or stator in a desired form.
When compared to the non-oriented electric steel sheets, amorphous metals provide excellent magnetic performance, but have been considered as being unsuitable for a long time for use in bulk magnetic members for a stator and a rotor for an electric motor because of faults occurring on particular physical properties and processing.
For example, the amorphous metals are thinner and harder than the non-oriented electric steel sheets, so fabrication tools and dies are worn more rapidly. An increase in the tooling and manufacturing costs may cause fabrication of bulk amorphous metal magnetic members to fail to have commercial competitiveness as compared to conventional techniques such as punching or stamping. The thickness of the amorphous metal may also come to an increase in the lamination number of the assembled members, and also increase the total cost of an amorphous metal rotor or stator magnet assembly.
The amorphous metals are fed into thin continuous ribbons having a uniform ribbon width. However, amorphous metals are very hard materials, and thus it is very difficult to easily mold or cut the amorphous metals. When the amorphous metal ribbons undergo an annealing process to ensure peak magnetic properties, the amorphous metal ribbons take on significantly great brittleness. This makes it difficult and costly to use conventional methods to form bulk amorphous magnetic members. In addition, the brittle amorphous metal ribbons lead to concerns about the durability of the bulk magnetic members in the application of electric motors.
Taking these points into consideration, Korean Patent Application Publication No. 2002-0063604 disclosed a low-loss amorphous metal magnetic component having a polyhedral shape and including multiple layer amorphous strips, for use in a high-efficiency electric motor. The amorphous metal magnetic component may be operated in a frequency range of about 50 Hz-20,000 Hz, has a core loss so as to exhibit improved performance characteristics compared with a silicon-steel magnetic component operating in the same frequency range as that of the amorphous metal magnetic component, and has a laminated structure with an epoxy after forming a plurality of cut strips having a predetermined length by cutting an amorphous metal strip in order to form a polyhedral shaped body.
However, the above-described Korean Patent Application Publication No. 2002-0063604 disclosed that the amorphous metal ribbons having still significant brittleness are prepared through a molding process such as a cut to thus cause a problem that it is difficult to make a practical application, and did not disclose a high-speed frequency application operating in a frequency range of 50 Hz-20,000 Hz.
Meanwhile, when implementing a high-speed motor of 50,000 rpm with a high-power of 100 kW such as a drive motor for an electric vehicle, by using silicon steel sheets, eddy current is increased due to high speed rotation to thereby cause a heat generation problem. In addition, since such a motor is fabricated in a large size, it is not applicable for a drive system of an in-wheel motor structure and it is not preferable in terms of increasing weight of the vehicle.
Typically, the amorphous strip has a low eddy current loss, but it is difficult to put a conventional core for a motor that is manufactured by winding or molding and laminating the amorphous strip to a practical use because of the difficulty of a manufacturing process as pointed out in the conventional art.
As described above, the prior art amorphous strip provides superior magnetic performance as compared to the non-oriented electrical steel sheet, but has not been used as the bulk magnetic member for a stator and a rotor for an electric motor because of defects occurring in the manufacturing process.
In view of this point, Korean Patent Application Publication No. 2013-0060239 disclosed a method of manufacturing a stator in which a plurality of split type stator cores are prepared by compression-molding amorphous metal powders and assembling the plurality of split type stator cores by using a bobbin. However, the degree of adhesion between the split type stator cores falls and thus there is a problem that the magnetic resistance is increased.
In addition, in the case of compression-molding amorphous metal powders to thereby prepare split type stator cores, the structure of a mold is complicated. Further, when the split type stator cores are coupled with each other, a coupling protrusion portion that forms a coupling structure may fall off due to a weak coupling strength.
Further, the conventional method of manufacturing stator cores by using amorphous cores has not proposed a design scheme of a magnetic core that is optimal to an electric motor field having high-power, high-speed, high-torque, and high-frequency characteristics.
Furthermore, a need for improved amorphous metal motor members indicating a combination of good magnetic and physical properties needed for high-speed, high-efficiency electric appliances has emerged. Development of a manufacturing method that can be performed for use of amorphous metals efficiently and for the mass production of various types of motors and magnetic components used therefor is required.
It is difficult to wind a slotted stator. In addition, the slotted stator requires a lot of time in the coil winding and requires complicated expensive coil winding equipment. In addition, a stator core having a plurality of teeth may have an advantage capable of using a low-cost general-purpose winding machine in the coil windings by assembling split type stator cores to prepare the stator core.
A drive motor for a drum type washing machine has required a slim-type drive motor because of a narrow installation space at the rear side of a tub. To meet the slimming requirement, it is necessary to reduce a core stack height in the axial direction to form a stator core and the height of the coil winding.
In addition, the larger core stack height is increased, and the coil winding length is increased to thereby increase a copper loss and also consumption of the coil wound thereto.
Further, when employing low-cost ferrite magnets for a rotor, instead of expensive Nd magnets, an overhang design that increases sizes of the magnets is applied for an increase of the motor efficiency. Accordingly, there is a problem that an end turn loss has occurred.
As described above, in the case of configuring a stator core with only a one-piece integration type core of a lamination type core and a compressed powder magnetic core, it is difficult to provide a stator of a high-speed, high-efficiency, thin and multi-slot structure.